The subject matter disclosed herein relates generally to imaging systems, and more particularly to methods and systems for reducing low-energy tails of a radiation detector.
Conventional radiation detectors receive one or more photons during an imaging session. The absorption of a photon represent an event that is collected by the radiation detector. When the radiation detector absorbs the photon a negative charge cloud of electrons and a positive charge cloud of holes are created. The negative charge cloud of electrons drifts toward the positively charged anode of the conventional radiation detector. The positive charge cloud of holes drifts toward the negatively charged cathodes of the radiation detector. The positive charge cloud moves slower relative to the negative charge cloud.
For any single event, the photon may be absorbed at various depths within the radiation detector. The depth is between the cathode or anode and a location where the photon, which is absorbed and referred to as a depth of interaction (DOI). A charge induced by the positive charge cloud on the cathode is negligible in some semiconductors, such as CdZnTe (CZT), which have low value of the product μτ for holes. The variable μ represents mobility, and the variable τ is the electron lifetime. The charge on the anode is proportional to the depth of a location of the event where the photon is absorbed.
The charge is associated with events, and are collected and recorded as corresponding energy values. During an imaging session of the radiation detector, multiple events are tracked and the corresponding energy values are recorded. The energy values for the events are analyzed to form one or more energy spectrums. The energy spectrums represent a count of a number of events at corresponding energy values of a select range (e.g., a histogram). The energy spectrum may be divided into a primary energy range and a low energy tail. The primary energy range is positioned to include a peak in the energy spectrum, while the low energy tail includes energy levels below the peak. The low energy tail reduces the efficiency of the radiation detector.
To reduce the low energy tail, conventional methods utilize: i) small anodes combined with a steering grid for creating a small pixel effect; ii) a co-planar grid including two interleaved grids that are biased by two different potentials to create a collecting and non-collecting grids (e.g., Luke grid); or iii) a small pixel effect combined with a signal derived from the cathode to calculate the DOI for applying electronic corrections. However, the conventional method of using the small anodes combined with the steering grid requires the use of many electronic channels. Conventionally, one electronic channel is coupled to each anode of the radiation detector. Accordingly, the use of small anodes requires the use of many anodes and electronic channels, which is a technical challenge. Additionally, the anodes require high voltage bias that is different from the high voltage bias applied to the steering grid, and the steering grid complicates the integration of the detector components due to interconnections and packaging.
Additionally, the conventional method of using the co-planar grid (e.g., the Luke grid) includes two high density grids interleaved together. The high density of the grids are necessary to create a similar response regardless of a location of the event. Accordingly, the conventional method is not useful for imaging purposes as it does not provide information on the event location. Further, the co-planar grid utilizes a permanent analog subtraction between the signals of the collecting and non-collecting grids for all of the events. The permanent analog subtraction decreases the signal-to-noise ratio for all of the events including events that do not need to be corrected by the co-planar grid. Additionally, the co-planar grid cannot be implemented with pixelated anodes as the co-planar grid requires a permanent analog differential subtraction between the pairs of pixels.